This invention relates to earth drilling rigs which are characterized by a mobile support or chassis upon which is mounted the drilling equipment and an elongated mast that is disposed for pivotal movement between a substantially horizontal transport position and an erect position for performing drilling operations.
In many drilling operations it is required that holes be drilled at various angles other than in the vertical direction and accordingly the drill rig may be provided with means for positioning the mast to provide the desired angular direction of the drill stem. Generally, prior art mounting arrangements for drilling slant holes have been characterized by telescoping braces and the like or other means wherein two relatively movable members are provided with a plurality of spaced openings in which pins are inserted once the openings in one member are aligned with the corresponding openings in the other member. Such arrangements are cumbersome and difficult to operate for selecting a predetermined angular position of the mast and they often require an assistant to the drill operator who must insert the locking pins while the operator handles the controls for the mast raising cylinders or the like to position the mast in the desired angular attitude.